PCM RF switch fabrication with subtractively formed heater

ABSTRACT

In fabricating a radio frequency (RF) switch, a heat spreader is provided and a heating element is deposited. A thermally conductive and electrically insulating material is deposited over the heating element. The heating element and the thermally conductive and electrically insulating material are patterned, where the thermally conductive and electrically insulating material is self-aligned with the heating element. A layer of an upper dielectric is deposited. A conformability support layer is optionally deposited over the upper dielectric and the thermally conductive and electrically insulating material. A phase-change material is deposited over the optional conformability support layer and the underlying upper dielectric and the thermally conductive and electrically insulating material.

RELATED APPLICATION(S)

The present application is related to U.S. patent application Ser. No.16/103,490, filed on Aug. 14, 2018, and titled “Manufacturing RF SwitchBased on Phase-Change Material,” and U.S. patent application Ser. No.16/103,587, filed on Aug. 14, 2018, and titled “Design for HighReliability RF Switch Based on Phase-Change Material.” The disclosuresof these related applications are hereby incorporated fully by referenceinto the present application.

BACKGROUND

Phase-change materials (PCM) are capable of transforming from acrystalline phase to an amorphous phase. These two solid phases exhibitdifferences in electrical properties, and semiconductor devices canadvantageously exploit these differences. Given the ever-increasingreliance on radio frequency (RF) communication, there is particular needfor RF switching devices to exploit phase-change materials. However, thecapability of phase-change materials for phase transformation dependsheavily on how they are exposed to thermal energy and how they areallowed to release thermal energy. For example, in order to transforminto an amorphous state, phase-change materials may need to achievetemperatures of approximately seven hundred degrees Celsius (700° C.) ormore, and may need to cool down within hundreds of nanoseconds. Thispresents a particular challenge for switching devices to preventdegradation due to high thermal energy while achieving fast switchingtimes.

Additionally, the ongoing need for miniaturization introduces upperlimits on driving voltages as well as overall device dimensions, oftencreating tradeoffs with parasitics associated with RF frequencies andresulting in performance tradeoffs. Accordingly, accommodating PCM in RFswitches can present significant manufacturing challenges. Specialtymanufacturing is often impractical, and large scale manufacturinggenerally trades practicality for the ability to control devicecharacteristics and critical dimensions.

Thus, there is a need in the art for reliably manufacturing low voltageand low parasitics PCM RF switches on a large scale.

SUMMARY

The present disclosure is directed to a phase-change material (PCM) RFswitch fabrication with subtractively formed heater, substantially asshown in and/or described in connection with at least one of thefigures, and as set forth in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an exemplary graph of phase-change material (PCM)temperature versus time according to one implementation of the presentapplication.

FIG. 1B illustrates a portion of an exemplary PCM radio frequency (RF)switch in an ON state according to one implementation of the presentapplication.

FIG. 1C illustrates an exemplary graph of switch resistance versusapplied pulse power according to one implementation of the presentapplication.

FIG. 2A illustrates an exemplary graph of PCM temperature versus timeaccording to one implementation of the present application.

FIG. 2B illustrates a portion of an exemplary PCM RF switch in an OFFstate according to one implementation of the present application.

FIG. 2C illustrates an exemplary graph of switch resistance versusapplied pulse power according to one implementation of the presentapplication.

FIGS. 3A and 3B illustrate a flowchart of an exemplary method formanufacturing a PCM RF switch according to one implementation of thepresent application.

FIGS. 4 through 20 each illustrate actions according to an exemplarymethod for manufacturing a PCM RF switch according to one implementationof the present application.

DETAILED DESCRIPTION

The following description contains specific information pertaining toimplementations in the present disclosure. The drawings in the presentapplication and their accompanying detailed description are directed tomerely exemplary implementations. Unless noted otherwise, like orcorresponding elements among the figures may be indicated by like orcorresponding reference numerals. Moreover, the drawings andillustrations in the present application are generally not to scale, andare not intended to correspond to actual relative dimensions.

Prior to a description of manufacturing methods according to the presentapplication, some relevant concepts in relation to radio frequency (RF)switches based on phase-change material (PCM) are discussed by referenceto FIGS. 1A through 2C. FIG. 1A illustrates an exemplary graph of PCMtemperature versus time according to one implementation of the presentapplication. As illustrated in FIG. 1A, PCM temperature-time graph 100includes trace 102 which represents the temperature of an “activesegment” of a PCM, such as active segment 119 of PCM 112 in FIG. 1B,plotted over time when a crystallizing heat pulse is applied to the PCM.It is noted that, according to the present application, “active segment”of the PCM is that portion of the PCM that undergoes a phase change inresponse to a crystallizing or an amorphizing heat pulse and generallylies between electrical contacts (or electrodes) on each end of the PCM,whereas the “passive segment” of the PCM is that portion of the PCM thatis generally not subject to a crystallizing or an amorphizing heat pulseand does not undergo a phase change. As shown in FIG. 1A, from time t0to time t1, trace 102 rises from initial temperature T₀ to approximatelyabove crystallization temperature T_(C). From time t1 to time t2, trace102 remains approximately above crystallization temperature T_(C). Fromtime t2 to time t3, trace 102 falls from approximately abovecrystallization temperature T_(C) to approximately initial temperatureT₀.

A heat pulse that holds the PCM at or above crystallization temperatureT_(C) for a sufficient amount of time will transform the PCM into acrystalline state. Accordingly, such a pulse may be referred to as acrystallizing pulse in the present application. Crystallizationtemperature T_(C) depends on the PCM material. In one implementation,crystallization temperature T_(C) can be approximately two hundreddegrees Celsius (200° C.). The amount of time needed to transform thePCM into a crystalline state depends on the material, dimensions,temperature, and thermal conductivity of both the PCM and itssurrounding structures. In one implementation, the time required can beapproximately one microsecond (1 μs) or greater or less. In the presentexemplary implementation, the duration from time t1 to time t2 in PCMtemperature-time graph 100 can be approximately one microsecond (1 μs),and thus, trace 102 represents a crystallizing pulse (trace 102 is alsoreferred to as crystallizing pulse 102 in the present application).

FIG. 1B illustrates a portion of an exemplary PCM RF switch according toone implementation of the present application. As illustrated in FIG.1B, PCM RF switch 110 includes PCM 112, input electrode 114, outputelectrode 116, and RF signal path (or simply referred to as “RF signal”)118. FIG. 1B illustrates PCM RF switch 110 after a crystallizing pulseis applied to PCM 112. PCM 112 can comprise germanium telluride(Ge_(X)Te_(Y)), germanium antimony telluride (Ge_(X)Sb_(Y)Te_(Z)),germanium selenide (Ge_(X)Se_(Y)), or any other chalcogenide. In variousimplementations, PCM 112 can be germanium telluride having from 40% to60% germanium by composition (i.e., Ge_(X)Te_(Y), where 0.4≤X≤0.6 andY=1−X). As shown in FIG. 1B, PCM 112 is uniform and is denoted with thelabel “x-PCM,” to indicate that PCM 112 is in the crystalline state. PCM112 in the crystalline state has low resistivity and is able to easilyconduct electrical current. Accordingly, RF signal 118 propagates alonga path from input electrode 114, through PCM 112, to output electrode116. It is noted that input electrode 114 and output electrode 116 canbe substantially symmetrical and that their roles in PCM RF switch 110can be reversed. PCM RF switch 110 in FIG. 1B is in an ON state.

FIG. 1C illustrates an exemplary graph of switch resistance versusapplied pulse power according to one implementation of the presentapplication. As illustrated in FIG. 1C, switch resistance-applied pulsepower graph 130 includes trace 132 that represents the resistance of PCMRF switch 110 in FIG. 1B, seen across input electrode 114 and outputelectrode 116, in response to a crystallizing pulse applied to PCM 112.As shown in FIG. 1C, when the pulse power increases past crystallizationpower We (i.e., past the power needed to heat PCM 112 to crystallizationtemperature T_(C)), switch resistance decreases from R_(OFF) to R_(ON)as shown by trace 132. In one implementation, crystallization powerW_(C) can be approximately three tenths of a Watt (0.3 W). In variousimplementations, R_(OFF) can range from approximately ten kilo-Ohms toapproximately one mega-Ohm (10 kΩ-1MΩ). In one implementation, R_(ON)can be approximately one Ohm (1Ω). Thus, trace 132 corresponds to PCM RFswitch 110 turning ON in response to a crystallizing pulse.

FIG. 2A illustrates an exemplary graph of PCM temperature versus timeaccording to one implementation of the present application. Asillustrated in FIG. 2A, PCM temperature-time graph 200 includes trace202 which represents the temperature of an “active segment” of a PCM,such as active segment 219 of PCM 212 in FIG. 2B, plotted over time whenan amorphizing heat pulse is applied to the PCM. It is noted that,according to the present application, “active segment” of the PCM isthat portion of the PCM that undergoes a phase change in response to acrystallizing or an amorphizing heat pulse and generally lies betweenelectrical contacts (or electrodes) on each end of the PCM, whereas the“passive segment” of the PCM is that portion of the PCM that isgenerally not subject to a crystallizing or an amorphizing heat pulseand does not undergo a phase change. As shown in FIG. 2A, from time t0to time t1, trace 202 rises from initial temperature T₀ to approximatelyabove melting temperature T_(M). From time t to time t2, trace 202remains approximately above melting temperature T_(M). From time t2 totime t3, trace 202 falls from approximately above melting temperatureT_(M) to approximately initial temperature T₀. Notably, from time t0 totime t3, trace 202 in FIG. 2A rises and falls more quickly than trace102 in FIG. 1A.

A heat pulse that melts and rapidly quenches the PCM from a temperatureat or above melting temperature T_(M) will transform the PCM into anamorphous state. Accordingly, such a pulse may be referred to as anamorphizing pulse in the present application. Melting temperature T_(M)depends on the PCM material. In one implementation, melting temperatureT_(M) can be approximately seven hundred degrees Celsius (700° C.). Howrapidly the PCM must be quenched in order to transform the PCM into anamorphous state depends on the material, dimensions, temperature, andthermal conductivity of both the PCM and its surrounding structures. Inone implementation, the quench time window can be approximately onehundred nanoseconds (100 ns) or greater or less. In this implementation,the duration from time t2 to time t3 in PCM temperature graph 200 can beapproximately one hundred nanoseconds (100 ns), and thus, trace 202represents an amorphizing pulse (trace 202 is also referred to asamorphizing pulse 202 in the present application).

FIG. 2B illustrates a portion of an exemplary PCM RF switch according toone implementation of the present application. As illustrated in FIG.2B, PCM RF switch 210 includes PCM 212, input electrode 214, outputelectrode 216, and RF signal path (or simply referred to as “RF signal”)218. FIG. 2B illustrates PCM RF switch 210 after an amorphizing pulse isapplied to PCM 212. PCM RF switch 210 in FIG. 2B generally correspondsto PCM RF switch 110 in FIG. 1B, and may have any of the implementationsand advantages thereof. As shown in FIG. 2B, PCM 212 is not uniform. PCM212 includes active segment 219, and passive segments 222. As usedherein, “active segment” refers to a segment of PCM that transformsbetween crystalline and amorphous states, for example, in response toheat pulses, whereas “passive segment” refers to a segment of PCM thatdoes not make such transformation and maintains a crystalline state(i.e., maintains a conductive state). Active segment 219 is denoted withthe label “α-PCM,” to indicate that active segment 219 is in theamorphous state. Passive segments 222 are denoted with the label“x-PCM,” to indicate that passive segments 222 are in the crystallinestate. PCM 212 in the amorphous state has high resistivity and is notable to conduct electrical current well. Accordingly, RF signal 218 doesnot propagate along a path from input electrode 214, through PCM 212, tooutput electrode 216. It is noted that input electrode 214 and outputelectrode 216 can be substantially symmetrical and that their roles inPCM RF switch 210 can be reversed. PCM RF switch 210 in FIG. 2B is in anOFF state.

FIG. 2C illustrates an exemplary graph of switch resistance versusapplied pulse power according to one implementation of the presentapplication. As illustrated in FIG. 2C, switch resistance graph 230includes trace 232 that represents the resistance of PCM RF switch 210in FIG. 2B, seen across input electrode 214 and output electrode 216, inresponse to an amorphizing pulse is applied to PCM 212. As shown in FIG.2C, when the pulse power increases past amorphization power W_(A) (i.e.,past the power needed to heat PCM 212 to melting temperature T_(M)),switch resistance increases from R_(ON) to R_(OFF) as shown by trace232. In one implementation, amorphization power W_(A) can beapproximately one and a half Watts (1.5 W). In various implementations,R_(OFF) can range from approximately ten kilo-Ohms to approximately onemega-Ohm (10 kΩ-1MΩ). In one implementation, R_(ON) can be approximatelyone Ohm (1Ω). Thus, trace 232 represents PCM RF switch 210 turning OFFin response to an amorphizing pulse.

FIG. 3A illustrates a portion of a flowchart of an exemplary method formanufacturing a PCM RF switch according to one implementation of thepresent application. Certain details and features have been left out ofthe flowchart that are apparent to a person of ordinary skill in theart. For example, an action may consist of one or more subactions or mayinvolve specialized equipment or materials, as known in the art.Moreover, some actions, such as masking and cleaning actions, areomitted so as not to distract from the illustrated actions. Actionsshown with dashed lines are considered optional. Actions 340 through 364shown in the flowchart of FIG. 3A are sufficient to describe oneimplementation of the present inventive concepts, other implementationsof the present inventive concepts may utilize actions different fromthose shown in the flowchart of FIG. 3A. Moreover, structures shown inFIGS. 4 through 16 illustrate the results of performing actions 340through 364 in the flowchart of FIG. 3A, respectively.

The method begins with action 340 by providing a heat spreader.Referring to FIG. 4, heat spreader 440 is provided over substrate 438.Heat spreader 440 may be any material with high thermal conductivity. Inone implementation, heat spreader 440 may be a material with both highthermal conductivity and high electrical resistivity. In variousimplementations, heat spreader 440 can comprise aluminum nitride (AlN),aluminum oxide (Al_(X)O_(Y)), beryllium oxide (Be_(X)O_(Y)), siliconcarbide (SiC), diamond, or diamond-like carbon. Heat spreader 440 can beprovided, for example, by physical vapor deposition (PVD), chemicalvapor deposition (CVD), or plasma enhanced chemical vapor deposition(PECVD). In one implementation, the thickness of heat spreader 440 isapproximately one micron (1 μm). In one implementation, substrate 438 isan insulator, such as silicon oxide (SiO₂). In various implementations,substrate 438 is a silicon (Si), silicon-on-insulator (SOI), sapphire,complementary metal-oxide-semiconductor (CMOS), bipolar CMOS (BiCMOS),or group III-V substrate. In one implementation, heat spreader 440itself performs as a substrate and a separate substrate is not used. Forexample, heat spreader 440 can comprise Si and be provided withoutsubstrate 438. In one implementation, heat spreader 440 can beintegrated with substrate 438.

The method optionally continues with action 342 by etching the heatspreader. Referring to FIG. 5, outer segments of heat spreader 440 areetched away, leaving sides 442. In one implementation, plasma dryetching is used for anisotropic etching of heat spreader 440 onsubstrate 438. In one implementation, the anisotropic etching in action342 leaves strain-relieving chamfers (not shown) at sides 442. It isnoted that action 342 is an optional action since heat spreader 440 doesnot have to be necessarily etched, and in some implementations heatspreader 440 can remain coextensive with substrate 438.

The method optionally continues with action 344 by depositing a lowerdielectric over the heat spreader. Referring to FIG. 6, lower dielectric444 is deposited over heat spreader 440 which is in turn situated oversubstrate 438. In one implementation, lower dielectric 444 is SiO₂. Inother implementations, lower dielectric 444 is silicon nitride(Si_(X)N_(Y)), or another dielectric. Lower dielectric 444 can bedeposited, for example, by PECVD or high density plasma CVD (HDP-CVD).In one implementation, the deposition thickness of lower dielectric 444can range from approximately one and a half microns to approximately twomicrons (0.5 μm-2 μm). Action 344 is optional in that the inventiveconcepts of the present application may be implemented withoutdepositing lower dielectric 444. For example, where action 342 ofoptionally etching heat spreader 440 is omitted, action 344 ofdepositing lower dielectric 444 can be omitted.

The method optionally continues with action 346 by planarizing the lowerdielectric. Referring to FIG. 7, lower dielectric 444 is planarized soas to have substantially planar top surface 446. In one implementation,chemical machine polishing (CMP) is used to planarize lower dielectric444. Substrate 438 underlies lower dielectric 444 and heat spreader 440.Action 346 is optional in that the inventive concepts of the presentapplication may be implemented without planarizing lower dielectric 444.For example, where action 344 of depositing lower dielectric 444 isomitted, action 346 of planarizing lower dielectric 444 can be omitted.

The method optionally continues with action 348 by etching the lowerdielectric. Referring to FIG. 8, lower dielectric 444 is etched down sothat top surface 448 of lower dielectric 444 is substantially coplanarwith heat spreader 440. Thus, the thickness of lower dielectric 444 willsubstantially match the thickness of heat spreader 440. For example, inone implementation, both the thickness of lower dielectric 444 afteretching and the thickness of heat spreader 440 are approximately onemicron (1 μm). In this implementation, heat spreader 440 may perform asan etch stop while lower dielectric 444 is selectively etched. In oneimplementation, reactive ion etching (RIE) is used to etch lowerdielectric 444. In one implementation, the RIE in action 348 leaves topsurface 448 of lower dielectric 444 below heat spreader 440, and thenCMP is used to touch polish heat spreader 440 so that heat spreader 440is substantially coplanar with top surface 448 of lower dielectric 444.Substrate 438 underlies lower dielectric 444 and heat spreader 440.Action 348 is optional in that the inventive concepts of the presentapplication may be implemented without etching lower dielectric 444. Forexample, where action 342 of optionally etching heat spreader 440 andaction 344 of optionally depositing lower dielectric 444 are omitted,action 348 of optionally etching lower dielectric 444 is moot and canthus be omitted.

The method optionally continues with action 350 by depositing a middledielectric over the heat spreader. Referring to FIG. 9, middledielectric 450 can be optionally deposited over lower dielectric 444 (incase optional lower dielectric 444 is utilized) and over heat spreader440. In one implementation, middle dielectric 450 is SiO₂. In otherimplementations, middle dielectric 450 is Si_(X)N_(Y), or anotherdielectric. Middle dielectric 450 can be deposited, for example, byPECVD or HDP-CVD. In one implementation, the thickness of middledielectric 450 is approximately 100 angstroms (100 Å). Substrate 438underlies lower dielectric 444 and heat spreader 440.

The method continues with action 352 by depositing a heating element.Referring to FIG. 10, heating element 452 is deposited over optionalmiddle dielectric 450. It is noted that in case optional middledielectric 450 is not used, heating element 452 can be depositeddirectly on heat spreader 440 (which may be a blanket unetched layer ofa high thermal conductivity material). Alternatively, in oneimplementation, heating element 452 can be deposited over lowerdielectric 444 (in case optional lower dielectric 444 is utilized) andover heat spreader 440, where middle dielectric 450 is not used.

In one implementation, heating element 452 can be deposited, forexample, by PVD. Heating element 452 can comprise any material capableof Joule heating that has a melting temperature higher than that of aPCM, such as PCM 464 in FIG. 16. Preferably, heating element 452comprises a material that exhibits little or substantially noelectromigration. In various implementations, heating element 452 cancomprise tungsten (W), molybdenum (Mo), titanium (Ti), titanium nitride(TiN), titanium tungsten (TiW), tantalum (Ta), nickel chromium (NiCr),or nickel chromium silicon (NiCrSi). For example, in one implementation,heating element 452 comprises tungsten lined with titanium and titaniumnitride. In one implementation, heating element 452 can have a thicknessof approximately five hundred angstroms to approximately five thousandangstroms (500 Å-5000 Å). As further shown in FIG. 10, substrate 438underlies lower dielectric 444 and heat spreader 440.

The method continues with action 354 by depositing a thermallyconductive and electrically insulating material over the heatingelement. Referring to FIG. 11, thermally conductive and electricallyinsulating material 454 is deposited over heating element 452. Thermallyconductive and electrically insulating material 454 may be any materialwith high thermal conductivity and high electrical resistivity. Invarious implementations, thermally conductive and electricallyinsulating material 454 can comprise AlN, Al_(X)O_(Y), Be_(X)O_(Y), SiC,Si_(X)N_(Y), diamond, or diamond-like carbon. Thermally conductive andelectrically insulating material 454 can be deposited, for example, byPVD, CVD, or PECVD. In one implementation, thermally conductive andelectrically insulating material 454 can have a thickness ofapproximately five hundred angstroms to approximately five thousandangstroms (500 Å-5000 Å). Also shown in FIG. 11 is middle dielectric 450that underlies heating element 452 and substrate 438 that underlieslower dielectric 444 and heat spreader 440.

The method continues with action 356 by patterning the heating elementand the thermally conductive and electrically insulating material.Referring to FIG. 12, outer segments of heating element 452 andthermally conductive and electrically insulating material 454 arepatterned, forming pattern 456. In this implementation, action 356 forpatterning heating element 452 and the thermally conductive andelectrically insulating material 454 may comprise two differentpatterning actions. In the first patterning action, thermally conductiveand electrically insulating material 454 can be patterned using achlorine-based dry etch. In the second patterning action, heatingelement 452 can be patterned using a fluorine-based dry etch. Bothpatterning actions can be performed using a single mask. As a result,heating element 452 and thermally conductive and electrically insulatingmaterial 454 will be self-aligned in pattern 456. In one implementation,action 356 for by patterning heating element 452 and the thermallyconductive and electrically insulating material 454 may comprise asingle patterning action. In various implementation, action 356 maycomprise partially or entirely patterning outer segments of middledielectric 450. In this implementation, heat spreader 440 may perform asa stop layer while middle dielectric 450 is selectively etched. Thematerials for heat spreader 440, middle dielectric 450, and the etchantused to pattern middle dielectric 450 can be chosen such that theetchant used to pattern middle dielectric 450 is highly selective ofmiddle dielectric 450 but stops at heat spreader 440. Further shown inFIG. 12 is substrate 438 that underlies lower dielectric 444 and heatspreader 440.

The method continues with action 358 by depositing a layer of an upperdielectric. Referring to FIG. 13, upper dielectric 458 is deposited overmiddle dielectric 450 and over pattern 456 (numbered in FIG. 12) ofheating element 452 and thermally conductive and electrically insulatingmaterial 454. In one implementation, upper dielectric 458 is SiO₂. Inother implementations, upper dielectric 458 is Si_(X)N_(Y), or anotherdielectric. Upper dielectric 458 can be deposited, for example, by PECVDor HDP-CVD. In one implementation, the deposition thickness of upperdielectric 458 can range from approximately one and a half microns toapproximately two microns (0.5 μm-2 μm). Further shown in FIG. 13 issubstrate 438 that underlies lower dielectric 444 and heat spreader 440.

The method continues with action 360 by planarizing the upper dielectricwith the thermally conductive and electrically insulating material.Referring to FIG. 14, upper dielectric 458 is substantially planarizedwith thermally conductive and electrically insulating material 454 toform planar surface 460. In one implementation, CMP is used to planarizeupper dielectric 458 with thermally conductive and electricallyinsulating material 454. In one implementation, CMP is used to planarizeupper dielectric 458 only, and then RIE is used to planarize upperdielectric 458 with thermally conductive and electrically insulatingmaterial 454. In one implementation, the RIE in action 360 leaves a topsurface of upper dielectric 458 below thermally conductive andelectrically insulating material 454, and then CMP is used to touchpolish thermally conductive and electrically insulating material 454 toform planar surface 460. In one implementation, any other planarizationtechnique may be used. Also shown in FIG. 14 is middle dielectric 450that underlies heating element 452 and substrate 438 that underlieslower dielectric 444 and heat spreader 440.

The method optionally continues with action 362 by depositing a“conformability support layer” over the upper dielectric and thethermally conductive and electrically insulating material. Referring toFIG. 15, conformability support layer 462 is deposited over upperdielectric 458 and thermally conductive and electrically insulatingmaterial 454. In one implementation, conformability support layer 462 isSi_(X)N_(Y). In another implementation, conformability support layer 462is SiO₂. Conformability support layer 462 can be deposited, for example,by PECVD or HDP-CVD. In one implementation, conformability support layer462 can have a thickness of approximately fifty angstroms toapproximately five hundred angstroms (50 Å-500 Å). According to thepresent application, “conformability support layer” is a homogenouslayer that allows a subsequent deposition to be substantially uniformwith respect to that layer. By optionally depositing conformabilitysupport layer 462, during a subsequent PCM deposition action, PCM can bedeposited on a homogenous surface, thereby allowing the PCM to besubstantially uniform with respect to that surface. If conformabilitysupport layer 462 were not used, subsequently deposited PCM would bedeposited on a non-homogeneous surface of thermally conductive andelectrically insulating material 454 and upper dielectric 458, andnonconformities are likely to occur in the subsequently deposited PCM,particularly around interfaces of thermally conductive and electricallyinsulating material 454 and upper dielectric 458. Also shown in FIG. 15is middle dielectric 450 that underlies heating element 452 andsubstrate 438 that underlies lower dielectric 444 and heat spreader 440.Action 362 is optional in that the inventive concepts of the presentapplication may be implemented without depositing conformability supportlayer 462.

The method continues with action 364 by depositing phase-changematerial. Referring to FIG. 16, PCM 464 is deposited over conformabilitysupport layer 462 (in case optional layer 462 is utilized) and overupper dielectric 458 and thermally conductive and electricallyinsulating material 454. PCM 464 can be germanium telluride(Ge_(X)Te_(Y)), germanium antimony telluride (Ge_(X)Sb_(Y)Te_(Z)),germanium selenide (Ge_(X)Se_(Y)), or any other chalcogenide. In variousimplementations, PCM 464 can be germanium telluride having from fortypercent to sixty percent germanium by composition (i.e., Ge_(X)Te_(Y),where 0.4≤X≤0.6 and Y=1−X). The material for PCM 464 can be chosen basedupon ON state resistivity, OFF state electric field breakdown threshold,crystallization temperature, melting temperature, or otherconsiderations.

PCM 464 can be deposited, for example, by PVD sputtering, CVD,evaporation, or atomic layer deposition (ALD). In one implementation,PCM 464 can have a thickness of approximately five hundred angstroms toapproximately two thousand angstroms (500 Å-2000 Å). In otherimplementations, PCM 464 can have any other thicknesses. The thicknessof PCM 464 can be chosen based upon sheet resistance, crystallizationpower, amorphization power, or other considerations. Further shown inFIG. 16 is middle dielectric 450 that underlies heating element 452 andsubstrate 438 that underlies lower dielectric 444 and heat spreader 440.

FIG. 3B is the remaining portion of the flowchart of FIG. 3Aillustrating an exemplary method for manufacturing a PCM RF switchaccording to one implementation of the present application. Certaindetails and features have been left out of the flowchart that areapparent to a person of ordinary skill in the art. For example, anaction may consist of one or more subactions or may involve specializedequipment or materials, as known in the art. Moreover, some actions,such as masking and cleaning actions, are omitted so as not to distractfrom the illustrated actions. Actions shown with dashed lines areconsidered optional. Actions 366 through 372 shown in the flowchart ofFIG. 3B are sufficient to describe one implementation of the presentinventive concepts, other implementations of the present inventiveconcepts may utilize actions different from those shown in the flowchartof FIG. 3B. Moreover, structures shown in FIGS. 17 through 20 illustratethe results of performing actions 366 through 372 in the flowchart ofFIG. 3B.

The method optionally continues with action 366 by depositing a contactuniformity support layer over the phase-change material. Referring toFIG. 17, contact uniformity support layer 466 is deposited over PCM 464.In one implementation, contact uniformity support layer 466 isSi_(X)N_(Y). Contact uniformity support layer 466 can be deposited, forexample, by PECVD or HDP-CVD. In one implementation, contact uniformitysupport layer 466 can have a thickness of approximately fifty angstromsto approximately two thousand angstroms (50 Å-2000 Å). By depositingcontact uniformity support layer 466 as shown in FIG. 17, during asubsequent etching of PCM contact holes, contact uniformity supportlayer 466 performs as an etch stop. In this implementation, etching PCMcontact holes may comprise two different etching actions. In the firstetching action, a contact dielectric, such as contact dielectric 472 inFIG. 20, can be aggressively etched to form most of the PCM contactholes. This first etching action can use a selective etch, for example,a fluorine-based plasma dry etch, and contact uniformity support layer466 can perform as an etch stop while contact dielectric 472 isselectively etched. In the second etching action, contact uniformitysupport layer 466 can be etched less aggressively. As a result, PCM 464will remain substantially intact, and uniform contact can be made to PCM464. Because the R_(ON) of a PCM RF switch, such as PCM RF switch 110 inFIG. 1B, depends heavily on the uniformity of contacts made with PCM464, the R_(ON) will be significantly lower when optional contactuniformity support layer 466 is used. In one implementation, contactuniformity support layer 466 is substantially thinner than contactdielectric 472. Action 366 is optional in that the inventive concepts ofthe present application may be implemented without depositing contactuniformity support layer 466.

The method continues with action 368 by etching the phase-changematerial. Referring to FIG. 18, outer segments of PCM 464 are etchedaway, leaving sides 468. In the present implementation, outer segmentsof contact uniformity support layer 466 and conformability support layer462 are also etched away. In one implementation, a fluorine-based plasmadry etch is used. By etching PCM 464 as shown in FIG. 18, a maximumchannel length of the PCM RF switch, and a maximum separation ofcontacts, can be determined.

The method optionally continues with action 370 by depositing apassivation layer over the etched phase-change material. Referring toFIG. 19, passivation layer 470 is deposited over PCM 464. In the presentimplementation, passivation layer 470 is also deposited over upperdielectric 458. In one implementation, passivation layer 470 is SiO₂. Inanother implementation, passivation layer 470 can be Si_(X)N_(Y).Passivation layer 470 can be deposited, for example, by PECVD orHDP-CVD. In one implementation, passivation layer 470 can have athickness of approximately fifty angstroms to approximately five hundredangstroms (50 Å-500 Å). Passivation layer 470 covers sides 468 (numberedin FIG. 18) of PCM 464. Action 370 is optional in that the inventiveconcepts of the present application may be implemented withoutdepositing passivation layer 470.

The method optionally continues with action 372 by depositing a contactdielectric over any optional passivation layer, and the underlyinglayers (including any optional underlying layers). Referring to FIG. 20,contact dielectric 472 is deposited over any optional passivation layer470, and any underlying optional contact uniformity support layer 466(numbered in FIG. 18), and PCM 464, and any optional conformabilitysupport layer 462 (numbered in FIG. 18). In one implementation, contactdielectric 472 is SiO₂. In other implementations, contact dielectric 472is Si_(X)N_(Y), or another dielectric. Contact dielectric 472 can bedeposited, for example, by PECVD or HDP-CVD. Referring to FIG. 20,contact dielectric 472 is planarized so as to have a substantiallyplanar top surface. In one implementation, CMP is used to planarizecontact dielectric 472. Action 372 is optional in that the inventiveconcepts of the present application may be implemented withoutdepositing contact dielectric 472.

By utilizing the methods disclosed in the present application, a PCM RFswitch employing phase-change material 464 can be reliably manufactured.Heat spreader 440 can perform as a stop layer during patterning ofheating element 452 and thermally conductive and electrically insulatingmaterial 454, and can remain in the final PCM RF switch to dissipateheat and quench PCM 464 after each heat pulse. Heating element 452 isdeposited using, for example, CMOS-compatible tungsten, and can receivecrystallizing pulse 102 and amorphizing pulse 202. Heating element 452is deposited with uniform thickness across wafers, resulting in uniformresistance in separate devices. Because thicker thermally conductive andelectrically insulating material 454 advantageously reduces C_(OFF)between PCM contacts, such as input electrode 114 or output electrode116 in FIG. 1B, and heating element 452, while thinner thermallyconductive and electrically insulating material 454 improves heattransfer between heating element 452 and PCM 464, the present methodsenable control over a critical design dimension. Further, becausethermally conductive and electrically insulating material 454 isdeposited directly over and patterned with heating element 452,thermally conductive and electrically insulating material 454 isself-aligned with heating element 452, allowing effective and efficientheat transfer to PCM 464. A PCM RF switch can therefore transitionbetween OFF and ON states using lower power and/or quicker pulses.

Depositing middle dielectric 450 biases vertical heat dissipation fromheating element 452 toward the active segment of PCM 464, rather thantoward heat spreader 440, enabling a PCM RF switch to transition betweenOFF and ON states using even lower power and/or even quicker pulses.Depositing conformability support layer 462 reduces nonconformities inPCM 464, thus improving reliability. Depositing contact uniformitysupport layer 466 advantageously reduces R_(ON).

Thus, various implementations of the present application achieve amethod of manufacturing a PCM RF switch that overcomes the deficienciesin the art. From the above description it is manifest that varioustechniques can be used for implementing the concepts described in thepresent application without departing from the scope of those concepts.Moreover, while the concepts have been described with specific referenceto certain implementations, a person of ordinary skill in the art wouldrecognize that changes can be made in form and detail without departingfrom the scope of those concepts. As such, the described implementationsare to be considered in all respects as illustrative and notrestrictive. It should also be understood that the present applicationis not limited to the particular implementations described above, butmany rearrangements, modifications, and substitutions are possiblewithout departing from the scope of the present disclosure.

The invention claimed is:
 1. A method of manufacturing a radio frequency (RF) switch, the method comprising: providing a heat spreader; depositing a heating element; depositing a thermally conductive and electrically insulating material over said heating element; patterning said heating element and said thermally conductive and electrically insulating material; depositing a layer of an upper dielectric; substantially planarizing said upper dielectric with said thermally conductive and electrically insulating material; depositing a conformability support layer over said upper dielectric and said thermally conductive and electrically insulating material; depositing a phase-change material over said conformability support layer.
 2. The method of claim 1, further comprising depositing a middle dielectric over said heat spreader prior to depositing said heating element, and wherein said heating element is deposited over said middle dielectric.
 3. The method of claim 1, wherein said conformability support layer comprises a material selected from the group consisting of silicon nitride (Si_(X)N_(Y)) and silicon oxide (SiO₂).
 4. The method of claim 1, wherein said thermally conductive and electrically insulating material is self-aligned with said heating element.
 5. The method of claim 1, wherein said phase-change material comprises a material selected from the group consisting of germanium telluride (Ge_(X)Te_(Y)), germanium antimony telluride (Ge_(X)Sb_(Y)Te_(Z)), germanium selenide (Ge_(X)Se_(Y)), and any other chalcogenide.
 6. The method of claim 1, wherein said heat spreader comprises a material selected from the group consisting of silicon (Si), aluminum nitride (AlN), aluminum oxide (Al_(X)O_(Y)), beryllium oxide (Be_(X)O_(Y)), silicon carbide (SiC), diamond, and diamond-like carbon.
 7. The method of claim 1, wherein said heat spreader performs as a stop layer during said patterning said heating element and said thermally conductive and electrically insulating material.
 8. The method of claim 1, further comprising depositing a contact uniformity support layer over said phase-change material.
 9. The method of claim 1, further comprising: etching said phase-change material; depositing a passivation layer over said etched phase-change material.
 10. A method of manufacturing a radio frequency (RF) switch, the method comprising: providing a heat spreader; depositing a middle dielectric over said heat spreader; depositing a heating element over said middle dielectric; depositing a thermally conductive and electrically insulating material over said heating element; patterning said heating element and said thermally conductive and electrically insulating material; depositing a layer of an upper dielectric; depositing a phase-change material over said upper dielectric and said thermally conductive and electrically insulating material.
 11. The method of claim 10, further comprising substantially planarizing said upper dielectric with said thermally conductive and electrically insulating material prior to said depositing said phase-change material.
 12. The method of claim 10, wherein said phase-change material comprises a material selected from the group consisting of germanium telluride (Ge_(X)Te_(Y)), germanium antimony telluride (Ge_(X)Sb_(Y)Te_(Z)), germanium selenide (Ge_(X)Se_(Y)), and any other chalcogenide.
 13. The method of claim 10, wherein said heat spreader comprises a material selected from the group consisting of silicon (Si), aluminum nitride (AlN), aluminum oxide (Al_(X)O_(Y)), beryllium oxide (Be_(X)O_(Y)), silicon carbide (SiC), diamond, and diamond-like carbon.
 14. The method of claim 10, wherein said heat spreader performs as a stop layer during said patterning said heating element and said thermally conductive and electrically insulating material.
 15. The method of claim 10, wherein said thermally conductive and electrically insulating material comprises a material selected from the group consisting of aluminum nitride (AlN), aluminum oxide (Al_(X)O_(Y)), beryllium oxide (Be_(X)O_(Y)), silicon carbide (SiC), silicon nitride (Si_(X)N_(Y)), diamond, and diamond-like carbon.
 16. The method of claim 10, further comprising depositing a contact uniformity support layer over said phase-change material.
 17. A method of manufacturing a radio frequency (RF) switch, the method comprising: providing a heat spreader; depositing a heating element; depositing a thermally conductive and electrically insulating material over said heating element; patterning said heating element and said thermally conductive and electrically insulating material, wherein said thermally conductive and electrically insulating material is self-aligned with said heating element; depositing a layer of an upper dielectric; depositing a phase-change material over said upper dielectric and said thermally conductive and electrically insulating material.
 18. The method of claim 17, wherein said phase-change material comprises a material selected from the group consisting of germanium telluride (Ge_(X)Te_(Y)), germanium antimony telluride (Ge_(X)Sb_(Y)Te_(Z)), germanium selenide (Ge_(X)Se_(Y)), and any other chalcogenide.
 19. The method of claim 17, wherein said heat spreader comprises a material selected from the group consisting of silicon (Si), aluminum nitride (AlN), aluminum oxide (Al_(X)O_(Y)), beryllium oxide (Be_(X)O_(Y)), silicon carbide (SiC), diamond, and diamond-like carbon.
 20. The method of claim 17, further comprising depositing a contact uniformity support layer over said phase-change material. 